1. Field of the Invention
This invention relates to an optical information recording-reproducing apparatus (hereinafter referred to as the optical disk apparatus) for effecting the recording and/or reproduction of information on a recording medium by the use of an optical head, and particularly to the structure of the optical head.
2. Related Background Art
An optical head in a prior-art optical disk apparatus is constructed as shown, for example, in FIG. 1 of the accompanying drawings.
In FIG. 1, the reference numeral 101 designates a fixed optical head fixed to an apparatus base for effecting the oscillation of a laser beam and the reproducing process of reflected light, the reference numeral 1 denotes a movable optical head for condensing and applying the laser beam from the fixed optical head onto a recording medium for the recording and/or reproduction of information and movable in the radial direction of a disk (the direction of arrow indicated in the figure), the reference numeral 2 designates an objective lens for condensing the laser beam on the surface of the recording medium, and the reference numeral 102 denotes a bending mirror for bending the laser beam emitted in parallel to the seek direction of the movable optical head from the fixed optical head in a direction perpendicular to the surface of the medium.
FIG. 2 of the accompanying drawings shows the details of the movable optical head shown in FIG. 1. In FIG. 2, reference numerals identical to those in FIG. 1 designate identical portions. Also, in FIG. 2, the reference numeral 3 denotes an actuator for driving the objective lens in the focusing and tracking directions of the recording medium, the reference numeral 5 designates a linear motor coil cooperating with a permanent magnet and a yoke, not shown (fixed to the apparatus side) to drive the movable optical head, and the reference numeral 103 denotes a bearing for receiving the guide, not shown, of the movable optical head. FIG. 3 of the accompanying drawings shows the details of the actuator shown in FIG. 2. In FIG. 3, the reference numeral 2 designates the objective lens, the reference numeral 10 denotes an objective lens holder, the reference numeral 11 designates a pin fixed to an optical head base, the reference numeral 12 denotes a tracking coil mounted on the objective lens holder 10, the reference numeral 13 designates a focusing coil, the reference numeral 14 denotes a permanent magnet, and the reference numeral 15 designates a yoke. In the above-described construction, by an electric current being supplied to the tracking coil 12, the objective lens holder 10 is rotated in the direction of arrow A about the pin 11. Thereby, the tracking of the laser beam is effected. Also, by an electric current being supplied to the focusing coil 13, the objective lens holder 10 is slid in the axial direction of the pin 11, i.e., the direction of arrow B, whereby the focusing of the laser beam is effected.
The seek operation of the optical head will now be described on the basis of the above-described construction. The entire movable optical head is first moved to near a desired position on the recording medium by a linear motor. At this time, the movable optical head is moved by the linear motor until a desired track falls within the movable range of the actuator in the direction of tracks by the number of transverse tracks and position detecting means such as an encoder. The desired track is then finely sought by the actuator, and when the laser spot arrives at the desired track, the laser spot is controlled to follow that track (tracking and focusing control), thus terminating the seek operation.
Now, to make the optical disk apparatus versatile in place of the present-day magnetic disk in the future, it is a requisite task to make the seek operation time of the above-described optical head as short as the seek operation time of the magnetic head.
For the realization of such speedup of the seek operation, it is requisite to make the movable optical head compact and light in weight, but the movable optical head of the above-described conventional construction carries thereon a complicated and large tracking and focusing actuator as shown in FIG. 3 and therefore, has structural limitations in the realization of its compactness and light weight, and this has led to the problem that the required speedup of the seek operation cannot be achieved.